This application relates to a control for air pressure supplied to assist an actuator in balancing forces on a linkage for controlling a nozzle cross-sectional area in a gas turbine engine.
A gas turbine engine includes a fan section, a compression section, a combustion section and a turbine section. An axis of the engine is centrally disposed along the engine and extends longitudinally through the sections. A primary flow path for working medium gases extends axially through the sections of the engine.
The nozzle for the gas turbine engine is typically provided with an actuation structure that can cause a plurality of flaps to pivot radially inwardly or outwardly to control the size of the nozzle opening. In the prior art, a hydraulic actuator drives a synchronous ring (“sync ring”), which is connected through linkages to the plurality of flaps. A control causes the actuator to move the flaps between various positions to provide a desired cross-sectional area.
In the prior art, it is also known to supply air pressure to a rear face of the sync ring to assist in handling a load on the actuation structure. In part, this load is created since there is relatively high engine air pressure within the nozzle, and acting on an inner surface of the flaps, and relatively low ambient pressure on an outer surface of the flaps. The high pressure supplied to the rear face of the sync ring assists in carrying some of this load. However, at times, the ratio between the pressure within the nozzle and the ambient pressure is much lower. As an example, at low speed/low altitude applications the ratio is typically low. In such applications there may be too much air pressure supplied to the sync ring.
Another feature which is often positioned adjacent the nozzle, is a liner ring which controls the flow of cooling air to the interior of the nozzle. The liner ring is rotated between a blocking position and an open position dependent on whether cooling air is necessary. Under certain conditions, such as when an aircraft is hovering, less cooling air is necessary. By blocking the flow of cooling air to the nozzle, additional cooling air is available for other purposes.